Wireless communication systems that utilize radio frequency carriers are well known in the art. Such systems offer services such as cellular telephone service, trunked dispatch services, paging services, and others. Recently, there has been a trend to offer multiple services on a single radio communication system. Some systems support subscriber units that offer both telephone interconnect and dispatch services, or telephone interconnect and paging services, among other combinations. The development of such systems have been evolutionary in nature. New services having differing characteristics are often grafted onto existing systems. Consequently, each service tends to have different access methodologies, including identifiers, initiation sequence, and the like. For example, when a user attempts a telephone call on a subscriber unit, the user acquires a dial tone, followed by the telephone number of the target communicant. When initiating a private call in dispatch mode to the same communicant, the user selects private call mode and enters a subscriber unit's dispatch identifier to initiate communications. Additionally, when the target communicant is a subscriber unit in a different radio system, a more complex call set up procedure is often necessary.
With the increasing demand for integrated services on a single subscriber unit of a radio communication system, subscriber units capable of communicating in multiple communication modes are becoming more widely available. It is desirable to facilitate communications between subscriber units regardless of communication modes. Therefore, an improved call set up procedure is needed for multi-mode communication devices.